Retrofit Air Tightness Cold Loft

[marone]

Currently refurbishing a property and looking at improving the air tightness of a cold loft using a membrane installed from above the joists on the loft side (much in the same way you would a suspended floor from above).  

 

I appreciate the easiest (and normal) way of doing this would be to remove the ceiling and attach the membrane to the bottom of the joists, however I have no plans to do this. Additional things to note is that there are led downlights throughout the ceiling and either sheepswool or hemp will be used to insulate the loft.

 

My thought was to keep the membrane tight to the joists and cut out the membrane around the downlights, then finally attaching further membrane around the downlights (JCC FGLED6 & FGLED10), perhaps forming a box around them?

 

Would placing the membrane over the joists in this way cause any problems? Damage joists, interstitial condensation etc...  
Would a vapour open (Solitex Plus?) or closed (Intello Plus?) membrane be better suited for this?

 

Thanks

Phil

[Declan52]

Main parts that will leak are around your lights and at the wall ceiling junction. First step would be to strip out whatever insulation you have in the loft so you can see where and holes or cracks are. Cracks can be easily covered with good airtightness tape with particular attention to the joins at the wall plate.

Holes where cables are coming through the plaster board you can squeeze silicone into the conduit or use the tape again. 

For spots I used clay plant pots. Looked into all kinds of pretty made units but they where very expensive compared to the 89p pot from b&q. I then used a grinder to cut a notch out of the rim for the cables then sealed the pot to the  ceiling using the tape again. 

There will be some bits usually under your water tank that you will have to use expanding foam to fill gaps as you can't get at them to use tape.

Don't forget the seal on the attic hatch.

I done all these steps in my last house and it made a real difference to heating upstairs. Took me a good two days. Once done then I rolled out all the insulation again . 

[Ferdinand]

In my view the problem with recessed spots is that they get installed in the first place.

 

You wouldn't consider getting rid?

 

The other issue I can see is protecting the membrane once installed.

 

Ferdinand

[marone]

Downlights will have to stay, I think the wife would force me to commit harikari if I suggested otherwise 

 

What do you mean about protection of the membrane? Once its down and the insulation is on top its unlikely to be disturbed, do you mean possible footfall damage over time when accessing the loft?

 

Thankfully there is no insulation in there at the moment so it makes things a little easier. I have started to foam the outer perimeters (gable ends so far) and plan to tape up the rest with Tescon Vana/No.1; then do the same to the inner edges where the stud walls are, same with service/pipe penetrations.

   

[PeterW]

21 minutes ago, marone said:

Downlights will have to stay, I think the wife would force me to commit harikari if I suggested otherwise 

 

Why don't you replace them with something like this..??

 

LED Downlights

[marone]

The downlights are all newly installed, replacing isn't really an option.

 

I'm more looking for advice around fitting a membrane... 

I know it would be a hassle and difficult to get right but would it be worthwhile? And if so should the membrane be open or closed, especially with the hygroscopic insulation that will be installed on the top. 

[Ferdinand]

8 hours ago, marone said:

Downlights will have to stay, I think the wife would force me to commit harikari if I suggested otherwise 

 

What do you mean about protection of the membrane? Once its down and the insulation is on top its unlikely to be disturbed, do you mean possible footfall damage over time when accessing the loft?

 

Thankfully there is no insulation in there at the moment so it makes things a little easier. I have started to foam the outer perimeters (gable ends so far) and plan to tape up the rest with Tescon Vana/No.1; then do the same to the inner edges where the stud walls are, same with service/pipe penetrations.

   

 

MY comment s based on penetration of and holes in membranes being a major problem with membranes hidden inside walls.

 

So an exposed membrane in a loft is more vulnerable imo.

 

What happens if they need to mend the roof from the inside?

 

Perhaps others know better.

 

F

[gravelld]

12 hours ago, marone said:

 

I have started to foam the outer perimeters (gable ends so far) and plan to tape up the rest with Tescon Vana/No.1; then do the same to the inner edges where the stud walls are, same with service/pipe penetrations.

   

You'll enjoy the eaves  if you have some scaffolding do it from outside. Best to use tape everywhere, foam won't last forever.

 

What you doing about pests?

 

Another way to look at it long term is that really the best solution will always be a warm loft with insulation outside of rafters and air tightness layer somewhere inbound of that, so if you have that vision then you could pass on the membrane for now and just do the basic work, everything else you have suggested: downlighters, service penetrations, ceiling/wall junctions etc.

Edited January 18, 2017 by gravelld